1. Field of the Invention
The present invention relates to a process for the manufacture of a trimer of an aliphatic aldehyde with a chlorinated 2-position.
2. Description of the Background Art
Monochloroacetaldehyde (hereinafter abbreviated to MCA), 2-chloropropionaldehyde (hereinafter abbreviated to CPA), 2-chlorobutyraldehyde (hereinafter abbreviated to CBA), and the like are known as aliphatic aldehydes with a chlorinated 2-position (hereinafter called 2-chloroaldehydes). These 2-chloroaldehydes are useful compounds as raw materials for the synthesis of organic compounds such as drugs, agrichemicals, and the like.
However, these 2-chloroaldehydes are unstable because of their possession of two functional groups; i.e., a high activity chlorine atom and an aldehyde group, in one molecule. Thus, it is difficult to stably store them for a long period of time. Technology for storing 2-chloroaldehyde in a stable manner for a long period of time is therefore desired.
In order to solve this problem, U.S. Pat. No. 5,008,462, for example, discloses that MCA can be stored as the trimer in a stable manner by the cyclic trimerization of MCA and that the trimer is easily regenerated into high purity MCA. This U.S. patent also discloses a process for manufacturing the MCA trimer.
According to the process for manufacturing the MCA trimer disclosed by U.S. Pat. No. 5,008,462, a chlorinated acetaldehyde solution containing MCA as a major component is dissolved into an organic solvent and reacted in the presence of concentrated sulfuric acid to produce MCA trimer. The same organic solvent and water are then added to the reaction mixture, in which part of the MCA trimer is present as crystals, in order to dissolve the crystals into the organic solvent and to separate a aqueous layer containing sulfuric acid. The organic layer is washed with water and the MCA trimer is recrystallized from the organic layer for separation.
Regarding the manufacture of CPA trimer, EP 0484 742 A1 discloses a method of trimerizing CPA by adding concentrated sulfuric acid to a mixture of a solution of chlorinated propionaldehyde and an organic solvent in the same manner as in the case of MCA.
These processes for the manufacture of MCA trimer or CPA trimer, in which the trimerization of 2-chloroaldehyde is carried out in the presence of concentrated sulfuric acid, however, involves difficulty in separating the produced trimer from concentrated sulfuric acid. Washing of the organic layer containing the trimer is required for the removal of concentrated sulfuric acid. Since unreacted 2-chloroaldehyde is easily soluble in water, not only the recovery of 2-chloroaldehyde is difficult, but also there are problems in the treatment of the waste water.